Step instability and surface mass transport strongly influence the kinetics of the two- to three-dimensional (2D–3D) transition in InAs/GaAs self-assembly epitaxy. In this paper we report evidence of the step erosion of quantum dots (QDs) nucleated on step edges for samples having different surface morphologies and the explosive nucleation of 3D QDs triggered by it. Related issues such as the temperature dependence of the critical thickness, the volume dependence of the surface mass transport, and the scaling behaviour are illustrated by means of RHEED and AFM measurements and data analysis for small increments of InAs coverage throughout the 2D–3D transition.

InAs quantum dots (QDs) self-assembled on GaAs(001) at the early stage of growth show scale invariance of the island size distribution, which have been interpreted in the framework of the Mulheran and Blackman theory. The central concept is the capture zone of the growing nucleus properly identified by the Voronoi' cells. We show that the volume distribution of the quantum dots well overlaps the area distribution of the associated Voronoi' cells determined experimentally. Moreover, we evidence that scale invariance takes place in a restricted range of coverage and, basically, thanks to a very fast nucleation process. By comparison between experimental data and numerical simulations of the growth, we determine the spatial correlation length among QDs. The key conditions for scale invariance to occur are pointed out, thus defining the range of validity of the model for application to other systems

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Results on an optical waveguide filter operating in the near IR region are reported. The device consists of a hybrid sol-gel -based grating loaded waveguide, obtained through the merging of conventional photolithography and UV-nanoimprinting. Starting from submicrometric gratings, fabricated by electron beam lithography, a soft mould has been produced and the original structures were replicated onto sol-gel photosensitive films. A final photolithographic step allowed the production of grating-loaded channel waveguides. The devices were optically characterized by transmission measurements in the telecom range 1450–1590 nm. The filter extinction ratio is −11 dB and the bandwidth is 1.7 nm.